Conventionally, motors comprising a rotor, a rotating shaft coupled with the rotor, and a balance weight fixed to an end surface of the rotor have been used as rotary machines for driving compressors used in air conditioners and other apparatuses. The balance weight reduces unbalanced forces acting on the rotating rotor. When the rotor is rotating in such rotary machines, centrifugal forces acting on the balance weight may cause the rotor to deform. The balance weight disclosed in Japanese Laid-open Patent Application No. 2007-205282 is configured to be capable of locking with the rotating shaft in order to minimize deformation of the rotor.